Method of separating chloronaphthalenes



July l1, 1933- E. c. BRITTON ET AL METHOD OF SEPARATING'CHLORONAPHTHALENES Filed May 21, 1930 gx N Q Ut 40 20 pemcantata-Clvloronaphfhalene lfm. m ,NIMH U m wm@ m 5l 0 .m 0 .HN. 8m w 1W amam .lm 50W L n. aL w60 ..Ire r m 1M C a Nw/m, d I. Y MH am A a u .rm...0.l Z .nl m l L dm, woo Jua." 2 a o L w .w c 0 o wv w WENT/R56 qu fBY mdf-amm @2ML Jwncw ATTORNEY Patented July 11, 1933 {UNITEDSTATESPATENT.. oFFlcE EDGAR c. DRIT'I'CN AND WILLIAM R. RRED,`CRMIDLAND,MICHIGAMAssICNoRs .'ro rIHR Dow CHEMICAL COMPANY,` or MIDLAND,MICHIGAN, A CORPORATION 0F MICHIGAN METHOD von sRPAR'ATINGcHLoRoNAPI-.ITI'IALENRS Application filed May 21, 1930. Serial No.454,303.`

The present invention relates to the separation of the alphaandbeta-monochloronaphthalenes from a mixture containing them, particularlyto a method involving the i crystallization of such componentsseparately from, for instance, a crude product obtained by chlorinatingnaphthalene.

Monochloronaphthalene prepared by the direct chlorination of naphthalenealways m hasgbeen supposedly a practically pure alphaates in the dye,pharmaceeuticalA and related fields.

Accordingly, our invention consists of the steps and product hereinafterfully described and particularly pointed outin the claims, the annexeddrawing and following description setting forth in detail certainprocedure whereby the principle of our invention may be utilized.

In said annexed drawing The single figure, in the form of a chart,diagrammatically shows the variation in the freezing point of mixturescomprising alphaand beta-chloronaphthalenes.V

' Itis impossible to separate the alphaand beta-chloronaphthalenes byfractional distillation thereof, the boiling points of the two isomersbeing only a few degrees apart, viz

258 and 264 C., respectively. However, we have found that theabove-mentioned monor chloronaphthalenes can be separated from eachother by means of controlled crystallization procedure, therebyaffording a practical 'separation method suitable for industrial use.Forinstance, an oil obtained through chlorinating naphthalene andconsisting subpreferred.

stantially of a mixture of alphaand betachloronaphthalenes, may becooled sufhciently to deposit crystals of the alpha modification,

a'temperature of alittle above 18 C., being The' `cooling may becontinued until practlcally all the alpha compound has form an eutecticmixture with the betaisomer present. The so crystallized substantiallypure alpha-chloronaphthalene may `then be separatedfrom the residualoil, for instance, by centrifuging the mixture at a temperature lowenough to preve11tresolution of the crystalline alpha form. f TheresidualV oil, consisting respectively of Vabout 7 5 and 25 per cent. ofthe alpha and beta compounds, may then be dissolved in a.suitablesolvent, e. g. methanol, absoluteethanolg-95 per cent. ethanol,acetone, isophopyl ether, chlorbenzene, carbontetrachloride, or analiphatic hydrocarbon, or a mixture thereof, and the so ob,- tainedsolution cooled to about 40 C., the

temperature depending -on the` kindV and 'I l amount of solvent used,whereby substantially pure beta-chloronaphthalene crystallizes out, andsuchbetaisomer may then be separated from the residual liquid.' VThelatter may be treated to remove eitherpart orall of the solvent therein,and the steps repeated until the-mixture of monochloronaphthalenes` hasbeen substantially separated into its components.

As. an alternative procedure, the originalV mixture ofmonochloronaphthalenes may be dissolved in a suitable solvent, such asabovev mentioned, :e. fg. an alcohol, the soobtained solution'cooled toabout 15 to 20 C., v crystallization induced and thethereby'crystallizedalpha compound separated from the lresidualsolution. The latter containing a larger proportion of the beta isomermay then be' diluted or not with more solvent and then be cooled toapproximately 30 to 40 C.,

and the thereby formed beta crystals4 separated from the liquor.

We further have found, that` a ,eutectic mixture of alphaandbeta-chloronaphthalenes may bedissolved in one'of the said ,solvents anda material crystallized out which contains a predominating amount-ofthebeta vbeen deposited, excepting that required to form. rllhis materialmay then be further crystallized from a solvent to obtain the componentsthereof.

The following examples illustrate ways in which our invention can beused i Example 1 p 500 grams of monochloronaphthalene,

freezing' at .-50 (l, and containing respec-- tively about 92 per centand 8 per cent =of the alpha andbeta isomers, was cooled to about V-15OC., crystallization induced, .and the crystals separated from the liquidby centrifuging. 340 grams of substantially purealpha-chloronaphthalene, melting at 2.5o C, were obtained, together'with160 Vgrams vof an oilconsistingrespectively'of about 75 per cent and 25per icent ofthe alpha and beta naodificaticms. -'Said latteroil wasdissolved in four times its Vweightwof ethanol, and cooledl to about1-400- C., wherebyl 30 gra-ms pure beta-chloronaphthalene wascrystallized and obtained by `filtration of 'the solution. 1 The latter,lwhich now= contained respectively about 120 grams vand-l() grams of thealpha and beta compounds, was substantiallyffreed ofv solvent byevaporation thereof and the above :steps were repeated until Iafterthreerepetitions of crystallization Vwithout a solvent followedby'crystallization `from a sol-V vent, `:the residual oil 'wasfreducedto about .20 grams.

p anlvproceeding as in Example l.L

ith 'mixtures in which the alpha isomer 'largely "predominates thepreferred pro- 'cedure willbe to separatelfirstithe .alpha isomerwhereby the 'residual solution is enriched in the beta isomer. Withmixtures approximating vthe eutectic composition suitable dilution `with'a solvent followed by cooling will permit separation of either alpha orbeta isomers 'depending upon composition,

' dilution andl temperature. With mixtures rich in the beta isomer, suchisomer'may be first separated and then the alpha isomer separated fromVtheV so enriched solution. Alternative procedures are also available asi illustrated in the examples.

The melting point of alpha-chloronaphthalene has neverbeen recorded inthe literature,

lalthough that of the corresponding beta compound, viz, k57 vC., isknown. We have found that the melting point' of the best comf mercialalpha compound, as produced according to the well known methods, doesnot exceed 50 C. However, the recrystalli'zed purealpha-chloronaphthalene obtained by rournew procedure, is found to havea somewhat 'higher melting point, viz. 2.50 C., such property thereby:affording a readily available and accurate means of determining thepurity of the alpha compound. Puri-A fied alphachloronaphthalene, asobtained throughour process, boils at 258.8o C. at 753 millimeterspressure and has the specific gravityll92 at 25" 1C. with respect towater aft i-@Q Our inventiomthen, involves methods'for the separation ofa mixture rolf alpha-fand betachloronaphthalenes into :componentsthereof, whereby thelatter :are obtained-'in substantially pure form,:and further, the

purification of lalphachloronaphthalene :re-

suit-ing from chlorination `of 'naphthalene-. Y Other modes of applyingthe v.principle of our invention :may be employed instead ofl the oneexplained, change being Vmade as regards the details, provided the `step=or steps stated by any of the following-eclaims or equivalent thereofIbe employed.

lllVe' 'therefore particularly point out and 'distinctly claim as Yourinventiony l. The method Lof separating 'alpha-'zandbeta-chloronaphthalenes from =a `mixture of said ycompounds inmon-eutectic proportions, which mixture may also contain `a* volatilezand substantially inert .organic solvent, which vcomprisescrystallizing fone of the isomerio -chloronaphthailenes bycooling the.mixture, separating the crystals ffromthe liquid, adjusting the quantityof organic solventrin `the mother liquorito such roporltion that-.theisomer which remained issolved during the above describedcry'stallization y'is least-soluble of the two isomers remaining in thesaid mother liquor, :and coolingthe yresultant solutiontoorys'tarllize-thesecond isomer. f

2..'Ihe method of separatingalphaand beta-chloronaplrthalenesY from' 'amixture thereof Vcontaining :alpha-chloronaphthaleno greater 'thaneutectic proportion, which ucomprises crystallizing out Aalpha compoundby cooling said Vvmixture, Vseparating theA crystals -from the liquid,vand then orystal- 120 lizing out beta fcompound-by' cooling ytheresidual mixture of alpha `and beta compounds v'dissolved ina-loweralcohol. A y

The lmethod ofseparating alphaand beta-chloronaphthalenes vfrom :aVmixture lthereof containing alpha-.chloronaphthalene in greater thanIeutectie proportion, which comprises `crystallizing 4out alpharcompoundcooling said mixture, separating .the

crystals from the liquid, and then crystallizi-ng outbeta'comfpoundbycoolingfthe residual mixture of alpha and beta compounds dissolved inmethyl alcohol.

4. The method of separating alphaand beta-chloronaphthalenes from amixture thereof containing alpha-chloronaphthalene in greater thaneutectic proportion, Which comprises crystallizing out alpha compoundlby cooling said mixture to about 15 C., separating the crystals fromtheliquid, and then crystallizing out beta compound by cooling theresidual mixture of alpha and beta compounds dissolved in methyl alcoholto a temperature of about 30 to 40 C.

`5. The method of separating alphaand beta-chloronaphthalenes from asolution thereof in a volatile and substantially inert organic solvent,Which solution initially contains alpha-chloronaphthalene in greaterthan eutectic proportion, Which comprises crystallizing outalpha-chloronaphthalene by cooling the solution, separating the crystalsfrom the liquid, diluting the mother liquor with a volatile andsubstantially inert organic solvent, and crystallizingv outbeta-chloronaphthalene by cooling the resultant solution.

6. The method of separating alphaand beta-chloronaphthalenes from asolution thereof in a loWer aliphatic alcohol, Which solution initiallycontains alpha-chloronaphthalene in greater than eutectic proportion,which comprises crystallizing outA alpha.- chloronaphthalene by coolingthe solution, separating the crystals from the liquid, diluting themother liquor with an additional quantity of a lower aliphatic alcohol,and crystallizing out beta-chloronaphthalene by cooling the resultantsolution. y

7. The method of separating alphaand beta-ch-loronaphthalenes from asolution thereof in methyl alcohol, Which'solution in'- itially containsalpha-chloronaphthalene in greater than eutectic proportion and containsmethyl alcohol in amount representing not more than about 30 per cent ofthe combined Weight -of the isomeric chloronaphthalene.

which comprises crystallizing out alphachloronaphthalene by cooling saidsolution to a temperature between about 15 and 20O C., separating thecrystals` from the V liquid, diluting the mother liquor With additionalmethyl alcohol, and crystallizing out beta-chloronaphthalene by coolingthe resultant solution to a temperature between about 30 and about 40 C.

8. In a method for the purification of alpha-chloronaphthalene, the stepwhich consists' in cooling a mixture of isomerio mono- "sists in coolingan alcoholic solution of isomerio mono-chloronaphthalenes, containingalpha-chloronaphthalene inv greater than eutecic proportion, toatemperature at Which alpha-chloronaphthalene crystallizes therefrom. y

10. In a method for the purification'of alpha-chloronaphthalene, thesteps which consist of crystallizing the same from a mixture of-isomeric mono-chloronaphthalenes, containing alpha-chloronaphthalene`in greater than eutectic proportion until only enough of the alphacompound remains in the mixture to form a eutectic compound With thevbeta isomer present, Vand separating the beta isomer by crystallizingthesame from a solution of they said eutectic in a volatilesubstantiallyinert solvent.

11. Asian articleof manufacture, alphachloronaphthalene in such a stateof purity as tohave a melting point of 2.5o C., a boiling point of258.8O CQunder 753 millimeters pressure, and a specific gravity of1.192at 25 @with respect to Water at 1 C.

12. The method ofseparating alphaand beta-choloronaphthalenes from amixture thereof containing alpha-choloronaphthalene in greater thaneutectic proportion, Which mixture may also contain a volatile andsubstantially inert organic solvent, Which comprises crystallizing outalpha-chloronaphthalene by cooling said mixture, separating the crystalsfrom the liquid, diluting the mother liquor With a volatile andsubstantially inert organic solvent, and crystalliz-v ing outbeta-chloronaphthalene by cooling the resultant solution.

Signed by us this 15th day of May, 1930. EDGAR C. 'BRITTON WILLIAM R.REED.

